In a CDMA mobile communication system, a mobile station sends an origination message or a paging response message when a system is in an access state, and then waits for an acknowledge message (BSOrder) from a base station, switches to a corresponding traffic channel according to the indication of an extended channel assignment message (ECAM) after receiving the ECAM, and starts to send a traffic channel prefix in a reverse traffic channel after receiving two continuous good frames. After receiving (capturing) the traffic channel prefix, the base station sends an origination handshake message (BSAckOrder) to the mobile station, and the mobile station replies a response handshake message (MSAckOrder). After receiving the response handshake message (MSAckOrder), the base station sends a service negotiation message to the mobile station, and then the mobile station replies a service negotiation accomplishment message. Then, the whole origination call flow ends and enters a call state. The process is as shown in FIG. 1.
During the whole origination call flow, within a certain period, if any one of the two parties in the communication does not receive the corresponding message, for example, the mobile station does not receive the ECAM from the base station, the base station does not receive the traffic channel prefix from the mobile station, the mobile station does not receive the origination handshake message (BSAckOrder) from the base station, the base station does not receive the response handshake message (MSAckOrder) from the mobile station, or the base station or the mobile station does not receive the service negotiation message from the opposite party, the call will be failed.
For every step of a call, there are many ways to solve the problem of call failure, such as sending the ECAM repeatedly, improving the power of sending the traffic channel prefix by the mobile station, or sending the handshake message repeatedly by the base station, and etc.
As shown by the dashed lines in FIG. 1, according to the call flow, the process that the base station receives the traffic channel prefix sent by the mobile station in the reverse traffic channel is a capture process. The process is the first interaction of the traffic channel between the base station and the mobile station, in which a general forward null frame is sent to the mobile station according to a fixed gain, and a general reverse open loop power control bits are set to a fixed value, that is to say, the reverse power control bits are the same for any user and any capture duration, and all the mobile stations within the coverage of the base station transmit the reverse traffic channel prefix by using the same power. Using this transmitting method, if the quality of the reverse link is poor, or a mobile station is far from the base station and located at the edge of the cell, or a mobile station suddenly enters a shadow area resulting in fast fading, it is easy to occur that the base station fails to capture the prefix of the mobile station or the mobile station very likely can not receive the null frame sent from the base station, which results in capture failure and thus results in the failure of the present call. In general, 70% of call failures are caused by the capture failure.
Therefore, there are some problems in the prior art which requires to be further improved.